Herbs, annual or perennial, rarely woody at base. Caulescent or acaulescent, stem hollow or solid. Leaves alternate, rarely opposite or basal; petiole usually sheathing at base; stipules absent (except in subfam. Hydrocotyloideae); leaf blade compound or sometimes simple, usually much incised or divided, pinnatifid to pinnatisect, or ternate-pinnately decompound. Flowers epigynous, small, bisexual or staminate (unisexual male), regular, in simple or compound umbels; umbellules few to many-flowered; rays often subtended by bracts forming a involucre; umbellules (sometimes called umbellets) usually subtended by bracteoles forming an involucel. Pedicels long, short or obsolete (then forming a capitate umbellule). Calyx tube wholly adnate to the ovary; calyx teeth (sometimes called sepals) small or obsolete, forming a ring around the top of the ovary. Ovary inferior, 2-celled, with one anatropous ovule in each locule. Styles 2, usually swollen at the base forming a stylopodium which often secretes nectar. Fruit dry, of two mericarps united by their faces (commissure), and usually attached to a central axis (carpophore), from which the mericarps separate at maturity; mericarps are variously flattened dorsally, laterally or terete; each mericarp has 5 primary ribs, one down the back (dorsal rib), two on the edges near the commissure (lateral ribs), and two between the dorsal and lateral ribs (intermediate ribs), occasionally with four secondary ribs alternating with the primary, the ribs filiform to broadly winged, thin or corky; vittae (oil-tubes) usually present in the furrow (intervals between the ribs sometimes called the valleculae) and on the commissure face, rarely also in the pericarp, sometimes obscure. Each mericarp 1-seeded, splitting apart at maturity. Seed face (commissural albumen) plane, concave to sulcate.

Although many members of this family have distinctive vegetative and floral features, providing a useful key to identify the many genera in China presents several difficulties. First, the classification of genera and generic groupings has been largely based on the morphology and anatomy of the fruit. Thus, to construct a “good” dichotomous key with equal leads, rather than “chipping off” individual genera using unique characteristics, the use of fruit macro- and microscopic characters is unavoidable. This is even more acute when dealing with large numbers of genera. Another major problem is that several of the large genera are heterogeneous, with diffuse generic boundaries and broad patterns of variation. To try and cope with these difficulties two types of identification tool are presented here. The first is a dichotomous key that emphasizes the traditional fruit characters, and the second is a multi-access key that allows easy comparison of ten characteristics across all genera. The multi-access key is particularly useful for incomplete material, but it is worth stressing that specimens without at least developing fruit are usually very difficult to identify.

Between 250 and 440(–455) genera and 3300–3700 species: widely distributed in the temperate zone of both hemispheres, mainly in Eurasia and especially in C Asia; 100 genera (ten endemic) and 614 species (340 endemic) in China.